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<title>EVP_RAND-CTR-DRBG</title>
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<ul id="index">
  <li><a href="#NAME">NAME</a></li>
  <li><a href="#DESCRIPTION">DESCRIPTION</a>
    <ul>
      <li><a href="#Identity">Identity</a></li>
      <li><a href="#Supported-parameters">Supported parameters</a></li>
    </ul>
  </li>
  <li><a href="#NOTES">NOTES</a></li>
  <li><a href="#EXAMPLES">EXAMPLES</a></li>
  <li><a href="#CONFORMING-TO">CONFORMING TO</a></li>
  <li><a href="#SEE-ALSO">SEE ALSO</a></li>
  <li><a href="#COPYRIGHT">COPYRIGHT</a></li>
</ul>

<h1 id="NAME">NAME</h1>

<p>EVP_RAND-CTR-DRBG - The CTR DRBG EVP_RAND implementation</p>

<h1 id="DESCRIPTION">DESCRIPTION</h1>

<p>Support for the counter deterministic random bit generator through the <b>EVP_RAND</b> API.</p>

<h2 id="Identity">Identity</h2>

<p>&quot;CTR-DRBG&quot; is the name for this implementation; it can be used with the EVP_RAND_fetch() function.</p>

<h2 id="Supported-parameters">Supported parameters</h2>

<p>The supported parameters are:</p>

<dl>

<dt id="state-OSSL_RAND_PARAM_STATE-integer">&quot;state&quot; (<b>OSSL_RAND_PARAM_STATE</b>) &lt;integer&gt;</dt>
<dd>

</dd>
<dt id="strength-OSSL_RAND_PARAM_STRENGTH-unsigned-integer">&quot;strength&quot; (<b>OSSL_RAND_PARAM_STRENGTH</b>) &lt;unsigned integer&gt;</dt>
<dd>

</dd>
<dt id="max_request-OSSL_RAND_PARAM_MAX_REQUEST-unsigned-integer">&quot;max_request&quot; (<b>OSSL_RAND_PARAM_MAX_REQUEST</b>) &lt;unsigned integer&gt;</dt>
<dd>

</dd>
<dt id="reseed_requests-OSSL_DRBG_PARAM_RESEED_REQUESTS-unsigned-integer">&quot;reseed_requests&quot; (<b>OSSL_DRBG_PARAM_RESEED_REQUESTS</b>) &lt;unsigned integer&gt;</dt>
<dd>

</dd>
<dt id="reseed_time_interval-OSSL_DRBG_PARAM_RESEED_TIME_INTERVAL-integer">&quot;reseed_time_interval&quot; (<b>OSSL_DRBG_PARAM_RESEED_TIME_INTERVAL</b>) &lt;integer&gt;</dt>
<dd>

</dd>
<dt id="min_entropylen-OSSL_DRBG_PARAM_MIN_ENTROPYLEN-unsigned-integer">&quot;min_entropylen&quot; (<b>OSSL_DRBG_PARAM_MIN_ENTROPYLEN</b>) &lt;unsigned integer&gt;</dt>
<dd>

</dd>
<dt id="max_entropylen-OSSL_DRBG_PARAM_MAX_ENTROPYLEN-unsigned-integer">&quot;max_entropylen&quot; (<b>OSSL_DRBG_PARAM_MAX_ENTROPYLEN</b>) &lt;unsigned integer&gt;</dt>
<dd>

</dd>
<dt id="min_noncelen-OSSL_DRBG_PARAM_MIN_NONCELEN-unsigned-integer">&quot;min_noncelen&quot; (<b>OSSL_DRBG_PARAM_MIN_NONCELEN</b>) &lt;unsigned integer&gt;</dt>
<dd>

</dd>
<dt id="max_noncelen-OSSL_DRBG_PARAM_MAX_NONCELEN-unsigned-integer">&quot;max_noncelen&quot; (<b>OSSL_DRBG_PARAM_MAX_NONCELEN</b>) &lt;unsigned integer&gt;</dt>
<dd>

</dd>
<dt id="max_perslen-OSSL_DRBG_PARAM_MAX_PERSLEN-unsigned-integer">&quot;max_perslen&quot; (<b>OSSL_DRBG_PARAM_MAX_PERSLEN</b>) &lt;unsigned integer&gt;</dt>
<dd>

</dd>
<dt id="max_adinlen-OSSL_DRBG_PARAM_MAX_ADINLEN-unsigned-integer">&quot;max_adinlen&quot; (<b>OSSL_DRBG_PARAM_MAX_ADINLEN</b>) &lt;unsigned integer&gt;</dt>
<dd>

</dd>
<dt id="reseed_counter-OSSL_DRBG_PARAM_RESEED_COUNTER-unsigned-integer">&quot;reseed_counter&quot; (<b>OSSL_DRBG_PARAM_RESEED_COUNTER</b>) &lt;unsigned integer&gt;</dt>
<dd>

</dd>
<dt id="properties-OSSL_DRBG_PARAM_PROPERTIES-UTF8-string">&quot;properties&quot; (<b>OSSL_DRBG_PARAM_PROPERTIES</b>) &lt;UTF8 string&gt;</dt>
<dd>

</dd>
<dt id="cipher-OSSL_DRBG_PARAM_CIPHER-UTF8-string">&quot;cipher&quot; (<b>OSSL_DRBG_PARAM_CIPHER</b>) &lt;UTF8 string&gt;</dt>
<dd>

<p>These parameters work as described in <a href="../man3/EVP_RAND.html">&quot;PARAMETERS&quot; in EVP_RAND(3)</a>.</p>

</dd>
<dt id="use_derivation_function-OSSL_DRBG_PARAM_USE_DF-integer">&quot;use_derivation_function&quot; (<b>OSSL_DRBG_PARAM_USE_DF</b>) &lt;integer&gt;</dt>
<dd>

<p>This Boolean indicates if a derivation function should be used or not. A nonzero value (the default) uses the derivation function. A zero value does not.</p>

</dd>
</dl>

<h1 id="NOTES">NOTES</h1>

<p>A context for CTR DRBG can be obtained by calling:</p>

<pre><code>EVP_RAND *rand = EVP_RAND_fetch(NULL, &quot;CTR-DRBG&quot;, NULL);
EVP_RAND_CTX *rctx = EVP_RAND_CTX_new(rand, NULL);</code></pre>

<h1 id="EXAMPLES">EXAMPLES</h1>

<pre><code>EVP_RAND *rand;
EVP_RAND_CTX *rctx;
unsigned char bytes[100];
OSSL_PARAM params[2], *p = params;
unsigned int strength = 128;

rand = EVP_RAND_fetch(NULL, &quot;CTR-DRBG&quot;, NULL);
rctx = EVP_RAND_CTX_new(rand, NULL);
EVP_RAND_free(rand);

*p++ = OSSL_PARAM_construct_utf8_string(OSSL_DRBG_PARAM_CIPHER,
                                        SN_aes_256_ctr, 0);
*p = OSSL_PARAM_construct_end();
EVP_RAND_instantiate(rctx, strength, 0, NULL, 0, params);

EVP_RAND_generate(rctx, bytes, sizeof(bytes), strength, 0, NULL, 0);

EVP_RAND_CTX_free(rctx);</code></pre>

<h1 id="CONFORMING-TO">CONFORMING TO</h1>

<p>NIST SP 800-90A and SP 800-90B</p>

<h1 id="SEE-ALSO">SEE ALSO</h1>

<p><a href="../man3/EVP_RAND.html">EVP_RAND(3)</a>, <a href="../man3/EVP_RAND.html">&quot;PARAMETERS&quot; in EVP_RAND(3)</a></p>

<h1 id="COPYRIGHT">COPYRIGHT</h1>

<p>Copyright 2020-2021 The OpenSSL Project Authors. All Rights Reserved.</p>

<p>Licensed under the Apache License 2.0 (the &quot;License&quot;). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at <a href="https://www.openssl.org/source/license.html">https://www.openssl.org/source/license.html</a>.</p>


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